Dry conditions and roving deer added extra challenge to intercropping in southwest Manitoba, but Melita’s Westman Agricultural Diversification Organization (WADO) still gleaned results this past season.
Intercropping, also known as companion cropping, is an emerging practice in general. Farmers are drawn to it for potential overyielding, disease or weed management or increased water use in wet years.
At the same time, dry years may drain subsoil moisture, a bad mix might pit crops against each other and a weather loss risks not just one crop, but two.
Added to that, the Manitoba Agricultural Services Corporation does not insure intercrops.
WADO hopes to clear up some of that risk.
The test farm near Melita ran intercropping trials this year on wheat-legume, pea-canola, hemp-legume and soybean-flax.
Wheat and legumes
One of the less novel mixes at WADO, wheat-legume has emerged as a cover crop option for producers who want to keep green cover after harvest, turn livestock out to graze or by organic producers to control weeds.
WADO hoped to single out best seeding practices. The farm compared both alfalfa and clover broadcast prior to spring wheat seeding, drilled into the furrow and broadcast after cereal was seeded.
Melita’s dry spring came into play on emergence, WADO manager Scott Chalmers said. Legumes seeded half an inch deep accessed moisture better, while broadcast seed did not respond until it rained.
Given that, Chalmers found seeding with the row was the best method and pre-seed broadcast followed, since the soil disturbance from wheat seeding worked in the legume.
“In the end, the biomass was basically the same despite whatever method you choose,” he said. “It’s more based on the seed viability depending on which treatment you pick.”
Respectively, in-row alfalfa and clover gave 381 and 279 kilograms of biomass per hectare compared to pre-seed broadcast (354 kg/ha for alfalfa and 168 kg/ha for clover) and post-seed broadcast (327 kg/ha in alfalfa, 267 kg/ha in clover).
WADO had some concern about yield lag in wheat, an issue that did not emerge, Chalmers said.
While pre-seed broadcast clover returned the lowest biomass, it also gave the highest wheat yield. The plot took off 4,374 kg/ha of wheat, beating out the control plot by 200 kg/ha. Others fell short of monocrop wheat, although the lowest yields (post-seed broadcast alfalfa and in-furrow clover) reached 3,870 kg/ha and kernel weights met or exceeded the check.
“I think if we had a better spring where we had a quick jump out of the ground, I think things would have been much different, but because of the delay, the wheat was really the main survivor and kind of overshadowed any effects that the legumes would have posed. We had a fantastic wheat yield,” Chalmers said.
Dr. Martin Entz of the University of Manitoba says those results match his own work in intercropping fall rye and legumes.
Like Chalmers, Entz found that adding legumes did not significantly impact yield and in-row seeding was better than broadcasting legumes.
Entz, however, also looked at soil type. Clay soils might give legumes a boost in a relay crop, Entz found in a 2001 study.
“Greater water-holding capacity of clay soils may make them better suited to late-season plant growth and less reliant on late-season precipitation than sandy soils,” the study read.
Pea and canola
Pea and canola trials were all about the fertilizer.
The second year WADO has tested the mix, researchers hoped to better understand dynamics between phosphorus and nitrogen.
Results echoed 2016, despite the drier year.
Once again, WADO found that any application of phosphorus benefited the crop, while nitrogen hindered nodulation in peas and gave canola a competitive advantage.
Combined 2016 and 2017 numbers showed that pea nodules declined from well over 30 per plant when no nitrogen was added to 20 with 90 pounds per acre of nitrogen.
In terms of phosphorus, a jump from no nutrient to 30 pounds per acre increased nodules from just over 20 to just under 30 per plant.
“Without phosphorus, it’s not going to do anything,” Chalmers said. “Any applied phosphorus was great not only for plant growth and grain yield but for nodulation as well, which was interesting… and any nitrogen we applied to the system really was not advantageous to grain yield.”
Jumping from no nitrogen to 45 pounds per acre did give several hundred kilograms more yield per hectare, mostly due to canola yield, although jumping again to 90 pounds per acre did not significantly increase production. Phosphorus had a constant upwards trend. The first 30 pounds of phosphorus per acre saw a similar yield jump as 45 pounds per acre of nitrogen, while 60 pounds per acre of phosphorus led to the highest yield jump of any single-nutrient plot. Plots with no phosphorus and 90 pounds per acre of nitrogen returned the lowest yields of any plot other than the unfertilized check.
“Any time we didn’t have phosphorus, it was detrimental to the system and it didn’t matter what rate of fertilizer for nitrogen that you put on,” Chalmers said.
The trial tagged 35 pounds per acre as an ideal phosphorus rate. Chalmers said land equivalence ratio, which compares crop yield if grown together with yields if you grew crops separately under the same management, plateaued at that point.
Entz was not surprised at those findings.
While he has not examined nitrogen in pea-canola himself, “what Scott has found seems logical,” he said. “The nitrogen fertilizer regime in legume/non-legume intercrops is an important question.”
Adding canola significantly dropped aphids in peas, WADO reported. Peas alone had almost 17 aphids per plant, compared to mixed plots which all saw less than four.
Soybean and flax
Soybean-flax yields will stay anecdotal, Chalmers said. WADO pulled back the trial after deer grazed plots enough that any samples would be invalid.
Flax visually overwhelmed the soybeans, however, Chalmers added. Flax thrived better in the dry conditions, particularly when planted in the same row as the pulse.
The early end also means that WADO couldn’t test soybean shelling during harvest. Chalmers previously expressed concerns that harvest speed for flax would damage soybeans.
WADO initially hoped that a flax-soybean mix would give similar disease advantages as flax and chickpea have demonstrated in Saskatchewan. The combination dropped chickpea aschocyta instance from 51 to 17 per cent during a 2014 South East Research Farm study.
Hemp and legumes
Hairy vetch showed the most promise, and the most risk, of the legumes mixed with hemp.
The trial also tested red clover, sweet clover, alfalfa. Two annual crops, fall rye and peas, were also planted.
“The hemp was the No. 1 crop,” Chalmers said. “The legumes did take, but once the hemp had bolted and had gone into flower, the legumes kind of took a second seat.”
Hairy vetch outstripped other legumes after hemp was taken off. Biomass topped 2,000 kg/ha of dry matter, while no other relay crop returned more than 500 kg/ha.
That same growth rate threatened harvest. Vetch grew high enough to tangle with seed heads and potentially plug combines.
“If you pick a tall variety, you’re probably not going to see much legume or vetch get up top, but if you’re picking a shorter variety, for example, Finola, I think the legume would have the upper hand and probably take over the crop.”
The effect may be even more dramatic on soil organic matter, according to Entz.
“Keep in mind that hairy vetch usually has three times more below growth than above-ground growth for the first six weeks of its life, so even an unimpressive amount of biomass of hairy vetch can make a big contribution,” he said.
Legumes and fall rye dragged yields slightly, with the exception of the poorly established red clover.
Field peas showed more promise for yield. The mix returned 909 kg/ha of hemp and 347 kg/ha of peas for the largest total grain yield.
“Certainly, there would be some issues with separating that crop because hemp is harvested so green,” Chalmers said.
The slight overyield might not be worth the inconvenience, he added, although a wetter year might see more pea yield.